ML20127E353
| ML20127E353 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood, Zion, 05000000 |
| Issue date: | 06/17/1985 |
| From: | George Alexander COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 0265K, 265K, GL-85-02, GL-85-2, NUDOCS 8506240527 | |
| Download: ML20127E353 (26) | |
Text
Commonwealth Edison ont First Natiortl PUza Chicigo. Illinois Address Reply to-Post Othee Box 767 Chicago, Illinois 60690 June 17, 1985 Mr. Harold R. Denton, Director Of fice of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Zion Station Units 1 and 2 Byron Station Units 1 and 2 Braidwood Station Units 1 and 2 Response to Generic Letter No. 85-02 Steam Generator Tube Integrity NRC Docket Nos. 50-295/304, 50-454/455 and 50-456/457 Reference (a):
Generic Letter 85 H. L. Thompson letter to all PWR OLS and CPS
Dear Mr. Denton:
This letter is provided in response to reference (a) which requested information concerning our program for steam generator tube integrity and steam generator tube rupture mitigation at our Zion, Byron, and Braidwood Stations.
Commonwealth Edison believes that safety related issues relative to steam generators are already addressed by. Standardized Technical Specifications.
However, we believe additional actions should be taken to improve plant availability and steam generator reliability.
To achieve this, the Company established a Steam Generator Task Force in 1982 to provide a corporate overview of steam generator activities at our PWR stations.
Representatives from Station Nuclear Engineering, Project Engineering, Zion Station, Byron Station, Braidwood Station and Westinghouse comprise the group which is chaired by an Assistant Vice President.
Our primary objective is to optimize the reliability of the steam generator and associated systems.
This is accomplished through periodic evaluation of steam generator conditions as reflected by plant operation, eddy current test results, and water chemistry data.
In addition, active participation in the the Steam Generator Owners Group has provided the Company with insight into tube degradation mechanisms, inspection program improvements, water chemistry improvements, steam generator material improvements, and stean generator thermal hydraulic analysis.
Attachments 1 through 3 to this letter are specific g
responses for our Byron, Braidwood, and Zion Stations.
There are 9"
significant differences in the answers to some of the questions
/
because the plants are of different vintages.
While the Zion Units I@
started operation in 1973 and 1974, Byron Unit i received its 100 per cent license this year, and the remaining Byron unit and the 8506240527 850617 PDR ADOCK 05000295 P
H.
R.
Denton June 17, 1985 Braidwood units are still under construction.
Without the benefit of inspections af ter a fuel cycle, our responses for Byron and Braidwood are necessarily limited to addressing the questions by referring to the Technical Specifications.
Currently, the contract package for the Byron Unit 1 eddy current inspection for the first refueling is being prepared; this activity will result in major interaction between the corporate task force and station personnel.
Until this activity is complete, the scope of inspections, beyond those required by the Technical Specifications, are tentative.
We believe it is therefore premature to detail the Byron and Braidwood programs beyond that contained in Attachments 1 and 2.
However, the final eddy current inspection programs for Byron and Braidwood will be developed with a philosophy similar to that used to develop the Zion eddy current inspection program.
The corporate task force recommends that certain inspections and actions be performed based on an evaluation of information referenced in the response to Enclosure 2 of the Generic Letter.
We believe that the current Zion program is the result of station review of these corporate recommendations coupled with their own experience.
Further, we believe that the Zion program is representative of the Company approach and anticipate that the Byron ano Braidwood programs will be similarly responsive to these issues.
However, it should not be inferred that the programs will be identical to our Zion program because the most important considerations are site specific operating experience and industry experience with similar steam generators.
These considerations will shape each plant specific steam generator eddy current inspection program. is a corporate response to Enclosure 2 which outlines the factors considereo in formulating a steam generator tube inspection program.
Please address any questions that you or your staff may have concerning our response to this office.
One (1) signed original with Attachment and fifteen copies are enclosed for your use.
Respectfully,
[
b.bn r G.L.
Alexander Attachments cc:
US NRC, Document Control Desk Washington, DC RIII Inspectors - Z/BY/BW 0265K
ATTACHMENT 1 Byron Station Response to Generic Letter 85-02 1.a PREVENTION AND DETECTION OF LOOSE PARTS (INSPECTIONS)
Staff Recommended Action Visual inspections should be performed on the steam generator secondary side in the vicinity of the tube sheet, both along the entire periphery of the tube bundle and along the tube lane, for purposes of identifying loose parts or foreign objects on the tubesheet, and external damage to peripheral tubes just above the tubesheet.
An appropriate optical device should be used (e.g., mini-TV camera, fiber optics).
Loose parts or foreign objects which are found should be removed from the steam generators.
Tubes observed to have visual damage should be eddy current inspected and plugged if found to be defective.
These visual inspections should be performed:
(1) for all steam generators at each plant at the next planned outage for eddy current testing, (2) after any secondary side modifications, or repairs, to steam generator internals, and (3) when eddy current indications are found in the free span portion of peripheral tubes, unless it has been established that the indication did not result frcm damage by a loose part of foreign object.
For PWR OL applicants, such inspections should be part of the preservice inspection.
For steam generator models where certain segments of the peripheral region can be shown not to be accessible to an appropriate optical device, licensees and applicants should implement alternative actions to address these inaccess1 Die areas, as appropriate.
Licensees should take appropriate precautions to minimize the potential for corrosion while the tube bundle is exposed to air.
The presence of chemical species such as sulfur may aggravate this potential, and may make exposure to the atmosphere inadvisable until appropriate remedial measures are taken.
Response
A preservice foreign object search and retrieval was performed on all four steam generators at Byron Station Unit 1 prior to placing the steam generators into service.
The search of secondary side of the steam generators was performed using inspection mirrors and fiberoptics. Visual Inspection Device access was gained through eleven of the twelve inspection holes on each steam generator (inspection was not performed through the wet lay-up nozzle hole).
. Byron Station does not plan to visually inspect the secondary side of the tube sheet at the next planned eddy current outage.
However, if secondary side modifications are performed or should eddy current testing reveal tube degradation in the periphery region with subsequent analysis indicating the presence of a loose part, an inspection of the secondary side will be conducted.
1.b PREVENTION AND DETECTION OF LOOSE PARTS (QUALITY ASSURANCE)
Staff Recommended Action Quality assurance / quality control procedures for steam generators should be reviewed and revised as necessary to ensure that an ef fective system exists to preclude introduction of foreign objects into either the primary or secondary side of the steam generator whenever it is opened (e.g.,
for maintenance, sludge lancing, repairs, inspection operations, modifications).
As a minimum, such procedures should include:
(1) detailed accountability procedures for all tools and equipment used during an operation, (2) appropriate controls on foreign objects such as eye glasses and film badges, (3) cleanliness requirements, and (4) accountability procedures for components and parts removed from the internals of major components (e.g.,
reassembly of cut and removed components).
Response
Byron Station has extensive administrative procedures in place to assure that no foreign objects are introduced or left in the steam generators, or any other vessel prior to its closure.
In addition, Byron Station has a Material Control Accountability Program for all of Unit 1 Containment.
All materials taken in or out of containment must be accounted for on Station Tools and/or Loose Parts Log, BAP 1450-T5.
In addition the loose parts monitoring system, includes four sensors on each steam generator two of which are on the secondary side.
. 2.a INSERVICE INSPECTION PROGRAM (FULL LENGTH TUBE INSPECTION)
Staff Recommended Action The Standard Technical Specifications (STS) and Regulatory Guide 1.83, Part C12.f, currently define a U-tube inspection as meaning an inspection of the steam generator tube from the point of entry on the hot-leg side.
The staff recommends that tube inspections should include an inspection of the entire length of the tube (tube end to tube end) including the hot-leg side, U-bend, and cold leg side.
This recommended action does not mean that the hot leg inspection sample and the cold leg inspections sample would necessarily involve the same tubes.
That is, it does not preclude making separate entries from the hot and cold leg sides and selecting different tubes on the hot and cold leg sides to meet the minimum sampling requirements for inspection.
Consistent with the current STS requirement, supplemental sample inspections (after the initial 3% sample) under this staff recommended action may be limited to a partial length inspection provided the inspection includes those portions of the tube length where degradation was found during initial sampling.
Response
The present Eddy Current Testing Program at Byron Station calls for inspections of steam generators from the hot leg side, around the U-bend, and to the top support on the cold leg side.
Full length examination of a number of steam generator tubes is planned to evaluate the effectiveness of repairs in the preheater region.
The scope of full length inspections is yet to be determined and will be dependent upon company and industry experience.
2.b INSERVICE INSPECTION PROGRAM (INSPECTION INTERVAL)
Staff Recommended Action The maximum allowable time between eddy current inspections of an individual steam generator should be limited in a manner consistent with Section 4.4.5.3 of the Standard Technical Specifications, and in addition should not extend beyond 72 months.
. Response:
Byron Station will examine their steam generators in accordance with W Standardized Technical Specification (STS) Section 4.4.5, Paragraph 4.4.5.3 (Inspection Frequencies).
This testing schedule calls for one steam generator to be examined once every 40 months (for Category C-1).
The extended inspection frequency is granted only if two consecutive inspection results fall within the C-1 category as having no additional tube degradation being detected.
Entrance into Category C-3 requires steam generator tube examinations to be conducted at a frequency no greater than once every 20 months.
3.a SECONDARY WATER CHEMISTRY PROGRAM Staff Recommended Action Licensees and applicants should have a secondary water chemistry program (SWCP) to minimize steam generator tube degradation.
The specific plant program should incorporate the secondary water chemistry guidelines in SGOG Special Report EPRI-NP-2704, "PWR Secondary-Water Chemistry Guidelines", October 1982, and should address measures taken to minimize steam generator corrosion, including materials selection, chemistry limits, and control methods.
In addition, the specific plant procedures should include progressively more stringent correct!.ve actions for out-of-specification water chemistry conditions.
These corrective actions should include power reductions and shutdowns, as appropriate, when excessively corrosive conditions exist.
Specific functional individuals should be identified as having the responsibility / authority to interpret plant water chemistry information and initiate appropriate plant actions to adjust chemistry, as necessary.
The referenced SG0G guidelines above were prepared by the Steam Generator Owners Group Water Chemistry Guidelines Committee and represent a consensus opinion of a significant portion of the industry for state-of-the-art secondary water chemistry control.
Response
Byron Station's Secondary Water Chemistry Program is based upon the CECO Nuclear Station Division Directive 501, "PWR Secondary Water Chemistry Control Program" This directive incorporates the SGOG guidelines.
At Byron Station, BAP 599-39 was written to implement the directive.
~5-3.b CONDENSER INSERVICE INSPECTION PROGRAM Staff Recommended Action Licensees should implement a condenser inservice inspection program.
The program should be defined in plant specific safety-related procedures and include:
1.
Procedures to implement a condenser inservice inspection program that will be initiated if condenser leakage is of such a magnitude that a power reduction corrective action is required more than once per three month period; and 2.
Identification and location of leakage source (s), either water or air; 3.
Methods of repair of leakage:
4.
Methodology for determining the cause(s) of leakage; 5.
A preventive maintenance program.
Response
1.
Byron has no procedure to implement an inspection program should condenser leakage be of such magnitude that a power reduction corrective action is required more than once per three months.
BOA Sec. 2 is the procedure that assigns action levels to condenser inleakage.
2.
There are. basically 2 areas of concern for inleakage sources, circulating water and air leakage.
a.
Byron previously had an approximately 1/2 GPM leak into condensate through the condenser tube to tube sheet rolled joint. We have since done extensive rework to eliminate problems encountered with leakage past the rolled condenser tubes into the condensate system at the tube sheet.
Both ends of all the condenser tubes have been internally bore welded and currently there is no measurable leakage, b.
Byron is equipped to measure air inleakage at the discharge of - the steam jet air ejectors (SJ AE).
The SJAE's remove all condensable gases from the main condenser.
. c.
Byron has an ongoing program to identify and resolve sources of condenser leakage and condensate dissolved oxygen.
4.
PRIMARY TO SECONDARY LEAKAGE LIMIT Staff Recommended Action All PWRs that have Technical Specifications limits for primary to secondary leakage rates which are less restrictive than the Standard Technical Specifications (STS) limits should implement the STS limits.
Response
The Byron Unit 1 Technical Specifications are based on the Westinghouse STS and are not less restrictive for leakage rates.
5.
COOLANT IODINE ACTIVITY LIMIT Staff Recommended Action PWRs that have Technical Specifications limits and surveillance for coolant iodine activity that are less restrictive than the Standard Technical Specification (STS) should implement the STS limits.
Those plants identified above that also have low head high pressure safety injection pumps should either:
(1) implement iodine limits which are 20% of the STS values, or (2) implement reactor coolant pump trip criteria which will ensure that if offsite power is retained, no loss of forced reactor coolant system flow will occur for steam generator tube rupture events up to and including the design basis double-ended break of a single steam generator tube, and implement iodine limits consistent with the STS.
Response
The Byron Station Technical Specifications are based on W STS.
The iodine activity limits for both the primary and secondary sides are the levels recommended and are therefore not less restrictive.
. 6.
SAFETY INJECTION SIGNAL RESET Staff Recommended Action The control logic associated with the safety injection pump suction flow path should be reviewed and modified as necessary, by licensees, to minimize the loss of safety function associated with safety injection reset during an SGTR event.
Automatic switchover of safety injection pump suction from the boric acid storage tanks (BAST) to the refueling water storage tanks should be evaluated with respect to whether the switchover should be made on the basis of low BAST level alone without consideration of the condition of the SI signal.
Response
This item is not applicable to Byron.
Byron SI pumps do not take suction from a BAST.
On receipt of an SI signal, the safety injection pumps immediately take suction from the RWST.
On a reset signal, the suction flow is not changed.
0265K
1 ATTACHMENT 2 Braidwood Station Response to Generic Letter 85-02 1.a PREVENTION AND DETECTION OF LOOSE PARTS (INSPECTIONS)
Staff Recommended Action Visual inspections should be performed on the steam generator secondary side in the vicinity of the tube sheet, both along the entire periphery of the tube bundle and along the tube lane, for purposes of identifying loose parts or foreign objects on the tubesheet, and external damage to peripheral tubes just above the tubesheet.
An appropriate optical device should be used (e.g., mini-TV camera, fiber optics).
Loose parts or foreign objects which are found should be removed from the steam generators.
Tubes observed to have visual damage should be eddy current inspected and plugged if found to be defective.
These visual inspections should be performed:
(1) for all steam generators at each plant at the next planned outage for eddy current testing, (2) after any secondary side modifications, or repairs, to steam generator internals, and (3) when eddy current indications are found in the free span portion of peripheral tubes, unless it has been established that the indication did not result from damage by a loose part or foreign object.
For PWR OL applicants, such inspections should be pjet of the preservice inspection.
For steam generator models where certain segments of the peripheral region can be shown not to be accessible to an appropriate optical device, licensees and applicants should implement alternative actions to address these inaccessible areas, as appropriate.
Licensees should take appropriate precautions to minimize the potential for corrosion while the tube bundle is exposed to air.
The presence of chemical species such as sulfur may aggravate this potential, and may make exposure to the atmosphere inadvisable until appropriate remedial measures are taken.
Response
Westinghouse performed a 3600 fiberoptic tubesheet annulus inspection following the drilling and machining of penetrations on the Unit 1 steam generators.
This activity was accomplished in January of 1981.
These steam generators were cleaned and approved by Westinghouse.
Currently, procedures are being developed to ensure against loose parts in the secondary side of the steam generators.
Inspections are planned in the preservice phase and the inservice phase, coincident with any secondary side modifications or repair activities.
,Y
+
i, r.
l' 1.b PREVENTION AND DETECTION OF LOOSE PARTS (QUALITY ASSURANCE)
Staff Recommended Action i
Quality assurance / quality control procedures for steam generators should be reviewed and revised as necessary to ensure that an effective system exists to preclude introduction of foreign objects into either the primary or secondary side of l
the steam generator whenever it is opened (e.g.,
for maintenance, sludge lancing, repairs, inspection operations, modifications).
As a minimum, such procedures should_ include:
(1) detailed accountability procedures for all tools and equipment used during an operation, (2) appropriate controls on foreign objects such as eye glasses and film badges, (3) z cleanliness requirements, and (4) accountability procedures for components and parts removed from the internals of major j
components (e.g., reassembly of cut and removed components).
j
Response
l The Braidwood Loose Parts Monitoring System includes 4 sensors on each steam generator, two of which are located on the secondary side.
In addition, BwMP 3300-T04 provides for control of tools and equipment used for work on the secondary side of the steam generators.
BwMP 3300-034, Open Reactor Coolant System Control Procedures, is being developed to address concerns over cleanliness, foreign object accountability and control, control of removed assemblies, and pre-closure inspections.-
2.a INSERVICE INSPECTION PROGRAM (FULL LENGTH TUBE INSPECTION)
Staf f Recommended Action The Standard Technical Specifications (STS) and Regulatory Guide 1.83, Part C.2.f, currently define a U-tube inspection as meaning an inspection of the steam generator tube from the point of entry on the hot-leg side completely around the U-Dend to the top support of the cold-leg side.
The staff recommends that tube inspections should include an inspection of the entire length of the tube (tube end to tube end) including the hot leg side, U-bend, and cold leg side.
This recommended action does not mean that the hot leg inspection sample and the cold leg inspection sample should necessarily involve the same tubes.
That is, it does not preclude making separate entries from the hot and cold leg sides and selecting different tubes on the hot and cold leg sides to meet the minimum sampling requirements for inspection.
. Consistent with the current STS requirement, supplemental sample inspections (after the initial 3% sample) under this staff recommended action may be limited to a partial length inspection provided the inspection includes those portions of the tube length where degradation was found during initial sampling.
Response
Braidwood is currently in the process of developing Technical Specifications.
These are based on Westinghouse STS and the Byron Technical Specifications, which call for tube inspections of the entire hot leg side, around the U-bend and down to the top support of the cold leg side.
We believe that this is adequate, given the greater propensity for tube degradation on the hot leg side.
However, a sample of tubes will have their full length inspected at the first refueling outage of Unit 1 to aid in evaluation of tube wear in the preheater region and the effectiveness of the Braidwood water chemistry control programs.
The scope of any subsequent full length inspections would be based on the results of this evaluation.
2.b.
INSERVICE INSPECTION PROGRAM (INSPECTION INTERVAL)
Staff Recommended Action The maximum allowable time between eddy current inspections of an individual steam generator should be limited in a manner consistent with Section 4.4.5.3 of the Standard Technical Specifications, and in addition should not extend beyond 72 months.
Response
The'Braidwood Technical Specifications which are currently being developed will require two steam generators to be inspected during the first inservice inspection.
The second and third ISI will each examine one steam generator not previously examined.
The fourth and subsequent ISI's may be limited to one steam generator each, on a rotating basis, provided that previous inspection results indicate similar performance of all steam generators.
When two consecutive inspections, exclusive of the preservice inspection, result in all inspection results falling into the j
. C-1 category, or if two consecutive inspections demonctrate that previously observed degradation has not progressed, the
-inspection interval may be extended to a maximum of once per 40 months.
The staff recommendation that inspection of an individual. steam generator should not extend beyond 72 months would not allow for one steam generator per inservice inspection to be examined.
This recommendation would cause at least two steam generators to have 6% of their tubes inspected each inservice inspection interval.
3.a SECONDARY WATER CHEMISTRY PROGRAM Staff Recommended Action Licensees and applicants should have a secondary water chemistry program (SWCP) to minimize steam generator tube degradation.
The specific plant program should incorporate the secondary water chemistry guidelines in SGOG Special Report EPRI-NP-2704, "PWR Secondary Water Chemistry guideli
's",
October 1982, and should address measures taken to minimize steam generator corrosion, including materials selection, chemistry limits, and control methods.
In addition, the specific plant procedures should include progressively more stringent corrective actions for out-of-specification water chemistry conditions.
These corrective actions should include power reductions and shutdowns, as appropriate, when excessively corrosive conditions exist.
Specific functional individuals should be identified as having the responsibility / authority to interpret plant water chemistry information and initiate appropriate plant actions to adjust chemistry, as necessary.
The referenced SGOG guidelines above were prepared by the Steam Generator Owners Group Water Chemistry Guidelines Committee and represent and consensus opinion of a significant portion of the industry for state-of-the-art secondary water chemistry control.
Response
The Braidwood Station Secondary Water Chemistry Program is based upon CECO Nuclear Stations Division Directive S01 "PWR Secondary Water Chemistry" which incorporates the SGOG guidelines.
BwCP PD-4, Braidwood Station Secondary Water Chemistry Program, implements the directive.
. 3.b CONDENSER INSERVICE INSPECTION PROGRAM Staff Recommended Action Licensees should implement a condenser inservice inspection program.
The program should be defined in plant specific safety-related procedures and include:
1.
Procedures to implement a condenser inservice inspection program that will be initiated if condenser leakage is of such a magnitude that a power reduction corrective action is required more than once per three month period; and 2.
Identification and location of leakage source (s), either water or air; 3.
Methods of repair of leakage; 4.
Methodology for determining the cause(s) of leakage; 5.
A preventive maintenance program.
Response
The condenser at Braidwood was tested for leakage between the shell and tubes in December of 1984.
Leaks were recorded and subsequently repaired.
BwVP 100-1, Testing the Condenser for Air Inleakage at 0% Power, is currently in the review process.
This procedure will be used to isolate the condenser, draw a vacuum, and test for air inleakage.
The need for additional surveillance requirements is currently being evaluated; the new surveillances, if deemed necessary, will be based upon Byron operating experience.
4.
PRIMARY TO SECONDARY LEAKAGE LIMIT Staf f Recommended Action All PWRs that have Technical Specifications limits for primary to secondary leakage rates which are less restrictive than tne Standard Technical Specification (STS) limits should implement the STS limits.
Response
The Braidwood Technical Specifications which are currently being developed will incorporate the STS limits for primary to secondary leakage.
]
. 5.
COOLANT IODINE ACTIVITY LIMIT Staff Recommend Action PWRs that have Technical Specifications limits and surveillance for coolant iodine activity that are less restrictive than the Standard Technical Specification (STS) should implement the STS limits.
Those plants identified above that also have low head high pressure safety injection pumps should either:
(1) implement iodine limits which are 20% of the STS values, or (2) implement reactor coolant pump trip criteria which will ensure that if of fsite power is retained, no loss of forced reactor coolant system flow will occur for steam generator tube rupture events up to and including the design basis double-ended break of a single steam generator tube, and implement iodine limits consistent with the STS.
Response
The Braidwood Techical Specifications which are currently being developed will implement the STS limits for coolant iodine activity.
Braidwood does not utilize low head high pressure SI pumps.
6.
SAFETY INJECTION SIGNAL RESET Staff Recommended Action The control logic associated with the safety injection pump suction flow path should be reviewed and modified as necessary, by licensees, to minimize the loss of safety function associated with safety injection reset during an SGTR event.
Automatic switchover of safety injection pump suction from the boric acid storage tanks (BAST) to the refueling water storage tanks should be evaluated with respect to whether the switchover should be made on the basis of low BAST level alone without consideration of the condition of the SI signal.
Response
This item is not applicable to Braidwood.
Braidwood SI pumps do not take suction from a BAST.
On receipt of an SI signal, the safety injection pumps immediately take suction from the RWST.
On a reset signal, the suction flow is not changed.
J
ATTACHMENT 3 Zion Station Response to Generic Letter 85-02 1.a PREVENTION AND DETECTION OF LOOSE PARTS (INSPECTIONS)
Staff Recommended Action Visual inspections should be performed on the steam generator secondary side in the vici..ity of the tube sheet, both along the entire periphery of the tube bundle and along the tube lane, for purposes of identifying loose parts or foreign objects on the tubesheet, and external damage to peripheral tubes just above the tubesheet.
An appropriate optical device should be used (e.g., mini-TV camera, fiber optics).
Loose parts or foreign objects which are found should be removed from the steam generators.
Tubes observed to have visual damage should be eddy current inspected and plugged if found to be defective.
These visual inspections should be performed:
(1) for all steam generators at each plant at the next planned outage for eddy current testing, (2) after any secondary side modifications, or repairs, to steam generator internals, and (3) when eddy current indications are found in the free span portion of peripheral tubes, unless it has been established that the indication did not result from damage by a loose part of foreign object.
For PWR OL applicants, such inspections should be part of the preservice inspection.
For steam generators models where certain segments of the peripheral region can be shown not to be accessible to an appropriate optical device, licensees and applicants should implement alternative actions to address these inaccessible areas, as appropriate.
Licensees should take appropriate precautions to minimize the potential for corrosion while the tube bundle is exposed to air.
The presence of chemical species such as sulfur may aggravate this potential, and may make exposure to the atmosphere inadvisable until appropriate remedial measures are taken.
Response
After any work in the steam generators on the secondary side is completed and before the permanent secondary side handhole covers are installed, a visual inspection of the tubesheet area on the secondary side of the steam generators is performed.
As much of the steam generator's center lane, annular area, and the tube lanes as can be seen is inspected for loose parts.
This is usually done by fiber optics but, if a contractor performs the job, he has the option to use a video camera or other means that meet our requirements.
Some concerns about these inspections are visibility and radiation exposure to personnel.
A typical visual inspection is limited to the tube lane, the annulus between the tubesheet and the bundle, and about 7-9 rows into the bundle.
Any loose parts in the center of the
'D' area of the bundle will go undetected.
The other concern, exposure, is under great scrutiny.
It is a major goal of the station to keep exposure to a minimum.
This inspection on several occasions has been a source of high exposure to the inspectors.
Zion Station has periodically conducted visual inspections since 1974.
There have been no eddy current indications of loose parts damage that can be seen by inspection.
If an eddy current indication appeared to be large enough and accessible enough for visual inspection, then an attempt would be made to inspect for it and determine its cause.
1.b PREVENTION AND DETECTION OF LOOSE PARTS (QUALITY ASSURANCE)
Staff Recommended Action Quality assurance / quality control procedures for steam generators should be reviewed and revised as necessary to ensure that an ef fective system exists to preclude introduction of foreign objects into either the primary or secondary side of the steam generator whenever it is opened (e.g.,
for maintenance, sludge lancing, repairs, inspection operations, modifications).
As a minimum, such procedures should include:
(1) cetailed accountability procedures for all tools and equipment used during an operation, (2) appropriate controls on foreign objects such as eye glasses and film badges, (3) cleanliness requirements, and (4) accountability procedures for compon'ents and parts removed from the internals of major components (edg.,<
reassembly of cut and removed components).
1
t V
(
t
Response
Zion Station has reviewed the procedures for work performed inside the steam generators and other work involving opening the I-primary system to verify their preclusion of introducing foreign j
objects into the steam generators or the primary system.
{
Zion Station has developed specific procedures for controlling
'the scope of work whenever it becomes necessary to remove and
,/
reinstall the steam generator primary and secondary manway i
covers or the primary and secondary handhole covers.
In addition, to controlling the work these procedures provide for
'V the utilization of the loose parts inventory procedure RC001-24 and the mechanical closure procedure P/M014-lN.
The RC001-24 procedure is used in conjunction with the maintenance procedures and provides direct accountability for all tools and equipment used on the job.
This includes a detailed loose parts inventory log documenting whatever enters and exits the primary system.
The procedure also provides control of other foreign objects such as eyeglasses or film f
badges.
Any parts removed from a primary system component are
'I also inventoried to ensure their removal from the system.
The
'RC001-24 procedure can be used for any job where control of parts and equipment entering and leaving an open system is desired.
Whenever RC001-24 is used for.the primary system the work process is monitored by the Quality Control Department who must also verify and approve the loose parts inventory log before any closure is allowed.
The mechanical closure procedure P/M014-lN is used for all closures and provides for a vise 1 internal loose parts inspection;os well as a seating surface cleanliness inspection.
These inspections are performed by the Quality Control Department and must be completed and approved before the closure-is allowed.
2.a INSERVICE INSPECTION PROGRAM (FULL LENGTH TUBE INSPECTION) t Staff Recommended Action The Standard Technical Specifications (STS) and Regulatory-Guide 1.83, Part C12.f, currently define a U-tube inspection as meaning an inspection of the steam generator tube from the point of entry on the hot-leg side.
The staff recommends that tube inspections should include an inspection of the entire length of the tube (tube end to tube end) including the hot-leg side, U-bend, and cold leg side.
L i
3.'
1
. i This recommended action does not mean that the hot leg inspection sample and the cold leg inspections sample would necessarily involve the same tubes.
That is, it does not v
preclude making separate entries from the hot and cold leg sides -
and selecting different tubes on the hot and cold leg sides to meet the minimum sampling requirements for inspection.
Consistent with the current STS requirement, supplemental samole inspections (after the initial 3% sample) under this staff recommended action may be limited to a partial length inspection-
-provided the inspection includes those portions of the tube length where degradation was found during initial sampling.
Response
Zion Station's overall program is essentially identical to the requirements of the Standard Technical Specifications and Regulatory Guide 1.83.
These requirements are considered to be,
minimum requirements.
Zion Station is currently testing essentially 100% of the tubes in each unit's four steam generators each outage.
The cnly exceptions have been tubes used for locating the eddy current fixture foot or tubes which are restricted (which are plugged if the obstruction canect; be removed).
Approximately 25% of the tubes in each generator are tested full length (tube end to tube end).
The evaluation of eddy current data is evaluated independently by two separate evaluators to minimize the possibility of errors.
Indications are additionally evaluated by a Level III eddy current evaluator.
The tubes selected for plugging are selected using Technical Specification criteria.
Pluggable tubes are retested for positive identification and marked for plugging.
Photographs of the tubesheet are taken efter marking tubes for plugging and again after plugging is complete to ensure that the proper tubes are plugged.
Zion Station currently examines approximately 900 tubes in each generator full length (tube end to tube end) eac,h outage.
Entry is from the hot leg side of the steam generator.
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. 2.b INSERVICE INSPECTION PROGRAM (INSPECTION INTERVAL)
Staff Recommended Action The maximum allowable time between eddy current inspections of an individual steam generator should be limited-in a manner consistent with Section 4.4.5.3 of the Standard Technical Specifications, and in addition should not extend beyond 72 months.
Response
Zion Station currently tests all four steam generators in each unit each outage.
This results nominally in one year between each inspection, although Zion is planning to go to 18 month
' fuel cycles.
Zion Station's current testing program is considered very conservative and is designed to assure unit reliability.
The testing will continua in this manner until it is felt that the conditions in the steam generators are sufficiently stable to allow a reduction in the magnitude or frequency of the testing.
Possible conditions that allow this are a stability or lack of growth of indication size and number, or mechanical or chemical changes to the steam generators.
3.a SECONDARY WATER CHEMISTRY PROGRAM 4
Staff Recommqnded Action Licensees and applicants should have a secondary water chemistry program (SWCP) to minimize steam generator tube degradation.
The specific plant program should incorporate the secondary water chemistry guidelines in SGOG Special Report EPRI-NP-2704, "PWR Secondary Water Chemistry Guidelines", October 1982, and should address measures taken to minimize steam generator corrosion, including materials selection, chemistry limits, and control methods.
In addition, the specific plant procedures should include progressively more stringent corrective actions for out-of-specification water chemistry conditions.
These corrective actions should include power reductions and shutdowns, as appropriate, when excessively corrosive conditions exist.
Specific functional individuals should be identified as having the responsibility / authority to interpret plant water chemistry information and initiate appropriate plant actions to y
adjust chemistry, as necessary.
4
. The referenced SG0G guidelines above were prepared by the Steam Generator Owners Group Water Chemistry Guidelines Committee and represent consensus opinion of a significant portion of the industry for state-of-the-art secondary water chemistry control.
Response
Zion Station was issued a Nuclear Stations Division Directive (NSDD) NSDD-S01 "PWR Secondary Water Chemistry Control Program" August 31, 1983.
The chemical control requirements as stated in the directive were derived from the EPRI - Steam Generators Owners Group Secondary Water Chemical Chemistry Guidelines, existing Westinghouse All Volatile Treatment guidelines, and known or suspected contaminant concerns.
The NSDD outlines specific functional individuals (including both station and corporate personnel) of their responsibility in the area of interpreting data, and their authority to initiate actions for secondary water chemistry control.
The procedures below were either written or revised for compliance with the NSDD.
1.
Zion Chemistry Procedure:
ZCP 311-1 Secondary System Analysis Requirements.
2.
Zion Chemistry Procedure:
ZCP 921-5 Secondary System Contamination.
3.
Abnormal Operating Procedure:
AOP-12 Secondary System Chemistry Excursion.
4.
Performance Test:
PT-0 Appendix 0, Operating Surveillance Checksheet.
AOP-12 includes the corrective actions for out of specification water chemistry.
The corrective actions do include power reductions and shutdowns, as appropriate, when excessive corrosive conditions exist.
3.b CONDENSER INSERVICE INSPECTION PROGRAM Staff Recommended Action Licensees should implement a condenser inservice inspection program.
The program should be defined in plant specific safety-related procedures and include:
J
. 1.
Procedures to implement a condenser inservice inspection program that will be initiated if condenser leakage is of such a magnitude that a power reduction corrective action is required more than once per three month period; and 2.
Identification and location of leakage source (s), either water or air; 3.
Methods of repair of leakage:
4.
Methodology for determining the cause(s) of leakage; 5.
A preventive maintenance program.
Response
Zion Station already has several non-safety related procedures that cover identifying and locating leakage into the condenser.
While the unit is on line, helium testing is used to locate air inleakage.
The off gas flow from the condenser, along with condenser pressure is monitored, and when a significant change occurs, the unit is checked to attempt to identify the new leakage source.
Also as part of trying to reduce the overall inleakage, a once per cycle test is done.
During the outage following the test, the leaks are repaired by repacking valves, changing gaskets, repairing welds, or using RTV in areas of suspected leakage.
After the outage, the repaired sources of leakage are tested to check the ef fectiveness of the repair.
-For water inleakage, helium testing can also be used.
The chemistry department monitors the condenser hotwell chemistry and trends the steam generator chemistry.
If an unusual reading is found, indicating a tube leak, helium is injected into the circulating water system waterbox that supplies the suspected area.
If helium is detected on the condenser shellside, the chemistry results are confirmed.
The next step is to identify the source (i.e., tube leak or tube to tubesheet leak).
A procedure exists that allows for waterbox inspections and testing for the leakage source while the unit is on line, with the approval of the load dispatcher.
If the unit is in an extended outage, as in refueling, the condenser can be hydrotested with a fluorescent red dye in order to identify leaks.
Also auring this test, all previously plugged tubes are verified to still have plugs.
This is done as often as we determine to be necessary.
. Also during extended outages, an extensive walkdown is done on the condenser shellside to inspect for any internal mechanical damage.
During the outage, work is done to repair any damage, and after all work is done on the condenser and LP turbine internals, a final walkdown is performed to inspect any repairs and remove any debris that may have been left behind.
Finally, at every other refueling outage, eddy current is done on a randomly selected set of condenser tubes.
This is to identify any pitting or corrosion to the tubing, or any mechanical damage and wear that cannot be visually spotted.
With these procedures and programs currently in place, air inleakage on one unit has been reduced dramatically, and the other unit is being studied.
Water inleakage has been a rare occurrence.
Sudden increases in either type of inleakage have been a very rare occurrence over the past few years.
4.
PRIMARY TO SECONDARY LEAKAGE LIMIT Staff Recommended Action All PWRs that have Technical Specifications limits for primary to secondary leakage rates which are less restrictive than the Standard Technical Specifications (STS) limits should implement the STS limits.
Response
Zion Technical Specification limits for primary to secondary leakage rates are identical to Standard Technical Specification limits.
No further action is required.
5.
COOLANT IODINE ACTIVITY LIMIT Staff Recommended Action PWRs that have Technical Specifications limits and surveillance for coolant iodine activity that are less restrictive than the Standard Technical Specification (STS) should implement the STS limits.
Those plants identified above that also have low head high pressure safety injection pumps should either:
(1) implement iodine limits which are 20% of the STS values, or (2) implement reactor coolant pump trip criteria which will ensure that if offsite power is retained, no loss of forced reactor coolant system flow will occur for steam generator tube rupture
. events up to and including the design basis double-ended break of a single steam generator tube, and implement iodine limits consistent with the STS.
Response
Zion Technical Specification (ZTS) limits and surveillance requirements for coolant iodine activity are identical to Standard Technical Specliications (STS) with only one exception.
,In the event that the specific activity of the primary coolant system exceeds the established limits, ZT.S require an isotopic analysis for I-131 through I-135 once per shift.
STS require an analysis for I-131, 1-133 and 1-135 every four hours.
This difference between ZTS and STS was reviewed and approved by the NRC on 4/19/84.
Zion Station employs medium head high pressure safety injection pumps.
Therefore, action statements regarding revised iodine limits and modifications to reactor coolant pump trip criteria are not applicable.
No further action is required.
6.
SAFETY INJECTION SIGNAL RESET Staff Recommended Action The control logic associated with the safety injection pump suction flow path should be reviewed and modified as necessary, by licensees, to minimize the loss of safety function associated with safety injection reset during an SGTR event.
Automatic switchover of safety injection pump suction from the boric acid storage tanks (BAST) to the refueling water storage tanks should be evaluated with respect to whether the switchover should be made on the basis of low BAST level alone without consideration of'the condition of the SI signal.
Response
Zion safety injection pump suction flow is normally from the refueling water storage tank.
During the recirculation phase following a LOCA, the pump suction path is realigned to the residual heat removal heat exchanger discharge.
Because safety injection pump suction is never aligned to boric acid storage tanks, the staff recommendation is not applicable and no further action is required.
Corporate Response to Enclosure 2 Information Requested The enclosed draft NUREG-0844 Section 2.2.1.2 describes certain limitations which the staf f believes to be inherent in the present Technical Specification steam generator ISI requirements pertaining to Category C-2 inspection results.
Licensees and applicants are requested to provide a description of their current policy and actions relative to this issue and any recommendations they have concerning how existing Technical Specification steam generator ISI reauirements pertaining to Category C-2 inspection results could be improved to better ensure that adequate inspections will be per formed.
This description should include a response to the following questions:
1.
What factors do, or would, the licensee or applicant consider in determining (1) whether additional tubes should be inspected beyond what is required by the Technical Specifications, (b) whether all steam generators should be included in the inspection program, and (c) when the steam generators should be reinspected.
2.
To what extent do these factors include consideration of the degradation mechanism itself and its potential for causing a tube to be vulnerable to rupture during severe transients or postulated accident before rupture or leakage of that tube occurs during normal operation.
Response
1.
In determining steam generator tube inspection sample size, the Company uses the Technical Specifications as the starting point.
The following factors are then used to evaluate the necessity of an expanded sample population to assure unit reliability during the upcoming cycle:
a.
steam generator experience on the particular unit to be inspected b.
past tube degradation and previous cycle operating experience on the particular unit to be inspected c.
company experience with steam generators and tube materials that are similar d.
industry wide tube degradation experience with steam generators of similar design, with similar tube materials, and/or support configurations relative to tube sheets, tube support plate and anti-vibration bars e.
specific steam generator design considerations such as model D4 and D5 preheaters f.
unit and industry wide trends are evaluated for type and rate of degradation for items a through e
Q These factors influence the number of tubes to be inspected, the
-number of steam generators to be inspected and the frequency of
' inspections.
For instance, the Zion Station eddy current program-is an example of the influence of these factors on the scope of inspection.
2.
These factors include an evaluation of the degradation mechanism based upon both unit operating experience and industry experience.
For unknown mechanisms, tubes are pulled to help gain' insight.into'the mechanism.
-For' example, at Zion, tube and anti-vibration bar samples pulled in 1983 helped identify the AVB wear mechanism.
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